FinFET devices having asymmetrical epitaxially-grown source and drain regions and methods of forming the same

ABSTRACT

Fin field-effect transistor (FinFET) devices and methods of forming the same are provided herein. In an embodiment, a FinFET device includes a semiconductor substrate having a plurality of fins disposed in parallel relationship. A first insulator layer overlies the semiconductor substrate, with the fins extending through and protruding beyond the first insulator layer to provide exposed fin portions. A gate electrode structure overlies the exposed fin portions and is electrically insulated from the fins by a gate insulating layer. Epitaxially-grown source regions and drain regions are disposed adjacent to the gate electrode structure. The epitaxially-grown source regions and drain regions have an asymmetric profile along a lateral direction perpendicular to a length of the fins.

TECHNICAL FIELD

The technical field generally relates to fin field-effect transistor(FinFET) devices and methods of forming the same, and more particularlyrelates to FinFET devices having an epitaxially-grown source and drainregions and methods of forming the FinFET devices having theepitaxially-grown source and drain regions.

BACKGROUND

Transistors such as metal oxide semiconductor field effect transistors(MOSFETs) or simply field effect transistors (FETs) are the corebuilding blocks of the vast majority of semiconductor integratedcircuits (ICs). A FET includes source and drain regions between which acurrent can flow through a channel under the influence of a bias appliedto a gate electrode that overlies the channel. Some semiconductor ICs,such as high performance microprocessors, can include millions of FETs.For such ICs, decreasing transistor size and thus increasing transistordensity has traditionally been a high priority in the semiconductormanufacturing industry. Transistor performance, however, must beimproved as the transistor size decreases.

A Fin field-effect transistor (FinFET) is a type of transistor thatlends itself to the dual goals of reducing transistor size whileincreasing transistor performance. The FinFET is a three dimensionaltransistor formed in a thin fin that extends upwardly from asemiconductor substrate. Transistor performance, often measured by itstransconductance, is proportional to the width of the transistorchannel. In a FinFET the transistor channel is formed along the verticalsidewalls of the fin or on both vertical sidewalls and the tophorizontal plane of the fin, so a wide channel, and hence highperformance, can be achieved without substantially increasing the areaof the substrate surface required by the transistor.

FinFETs provide a promising candidate for small line width technology(e.g., approximately 22 nm and below) because of their excellent shortchannel effect control and scalability. Epitaxially-grown source anddrain regions are often formed for the FinFETs by replacing portions ofthe fin with epitaxially-grown material. The epitaxially-grown sourceand drain regions may be employed to provide either compressive ortensile strain (depending upon whether a P-type FinFET or N-type FinFETis to be formed) within a channel of the FinFETs. The channel is theregion of the fin disposed under a gate electrode structure and betweenthe source region and the drain region. Compressive strain and tensilestrain serve to increase hole mobility or electron mobility,respectively, within the channel. For example, the epitaxially-grownsource and drain regions may include silicon germanium (SiGe) to providecompressive strain within the channel, thereby resulting in enhancedhole mobility that is desirable for P-type FinFETs. As another example,the epitaxially-grown source and drain regions may include siliconcarbon (SiC) or/and silicon carbon phosphorous (SiC:P) to providetensile strain within the channel, thereby resulting in enhancedelectron mobility that is desirable for N-type FinFETs.

To form the epitaxially-grown source and drain regions, portions of thefin adjacent to the gate electrode structure are etched to formtrenches, followed by epitaxially growing the appropriate material(depending upon whether P-type FinFETs or N-type FinFETs are to beformed) in the trenches. To selectively expose portions of the fin wheretrenches are to be formed, a hard mask is patterned to define gaps wherethe trenches are to be formed. Sidewall spacers formed from material ofthe hardmask remain disposed adjacent to the fin after patterning andafter formation of the trenches. Epitaxial growth generally propagatesboth vertically and laterally, with the epitaxially-grown materialgrowing over the sidewall spacers and toward epitaxially-grown sourceand drain regions of adjacent fins, often resulting in merger of theepitaxially-grown source and drain regions of adjacent fins. Merger ofthe epitaxially-grown source and drain regions of adjacent fins willresult in failure for single fin devices (where multiple adjacent finseach include separate transistors). Avoiding merger of epitaxially-grownsource and drain regions of adjacent fins becomes more difficult as linewidth technology continues to scale down, with distances between finsbecoming smaller and smaller. Further, efforts to minimize a profile ofthe epitaxially-grown source and drain regions results in less availablesurface area of the epitaxially-grown source and drain regions forformation of silicide, thereby possibly compromising effectiveelectrical connection to the epitaxially-grown source and drain regionsespecially as line width technology continues to scale down.

Accordingly, it is desirable to provide FinFET devices and methods offorming such FinFET devices that avoid merger between epitaxially-grownsource and drain regions of adjacent fins while also maximizingavailable surface area of the epitaxially-grown source and drain regionsfor formation of silicide, even as line width technology continues toscale down. Furthermore, other desirable features and characteristics ofthe present invention will become apparent from the subsequent detaileddescription of the invention and the appended claims, taken inconjunction with the accompanying drawings and this background of theinvention.

BRIEF SUMMARY

Fin field-effect transistor (FinFET) devices and methods of forming thesame are provided herein. In an embodiment, a FinFET device includes asemiconductor substrate having a plurality of fins disposed in parallelrelationship. A first insulator layer overlies the semiconductorsubstrate, with the fins extending through and protruding beyond thefirst insulator layer to provide exposed fin portions. A gate electrodestructure overlies the exposed fin portions and is electricallyinsulated from the fins by a gate insulating layer. Epitaxially-grownsource regions and drain regions are disposed adjacent to the gateelectrode structure. The epitaxially-grown source regions and drainregions have an asymmetric profile along a lateral directionperpendicular to a length of the fins.

In another embodiment, a fin field-effect transistor device includes asemiconductor substrate having a plurality of fins disposed in parallelrelationship. A first insulator layer overlies the semiconductorsubstrate, with the fins extending through and protruding beyond thefirst insulator layer to provide exposed fin portions. A gate electrodestructure overlies the exposed fin portions and is electricallyinsulated from the fins by a gate insulating layer. Epitaxially-grownsource regions and drain regions are disposed adjacent to the gateelectrode structure. A first sidewall spacer is disposed adjacent to afirst side of the fins and directly over the first insulator layer.Optionally, a second sidewall spacer is disposed adjacent to a secondside of the fins and over the first insulator layer, wherein whenpresent the second sidewall spacer is smaller than the first sidewallspacer. Portions of the epitaxially-grown source regions and drainregions are further disposed overlying a top of the first sidewallspacer and a top of the second sidewall spacer when present.

In another embodiment, a method of forming a FinFET device includesproviding a semiconductor substrate having a plurality of fins with afirst insulator layer overlying the semiconductor substrate, with thefins extending through and protruding beyond the first insulator layerto provide exposed fin portions, and with a gate electrode structureoverlying the exposed fin portions and electrically insulated from thefins by a gate insulating layer. A first intermediate sidewall spacer isformed adjacent to the first side of the fins and over the firstinsulator layer and a second intermediate sidewall spacer adjacent tothe second side of the fins and over the first insulator layer. Thesecond intermediate sidewall spacer is asymmetrically etched as comparedto the first intermediate sidewall spacer to produce a first sidewallspacer and optionally a second sidewall spacer adjacent to a sourceregion and a drain region in the fins, wherein when present the secondsidewall spacer is smaller than the first sidewall spacer. Portions ofthe fins adjacent to the gate electrode structure are etched with a finetchant to form trenches. Semiconductor material is epitaxially grown inthe trenches to form epitaxially-grown source regions and drain regions,wherein portions of the epitaxially-grown source regions and drainregions are further disposed overlying a top of the first sidewallspacer and a top of the second sidewall spacer when present.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will hereinafter be described in conjunctionwith the following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 is a perspective view of a portion of a semiconductor substrateincluding a plurality of fins and a gate electrode structure overlyingthe fins;

FIGS. 2-6 are cross-sectional side views of the semiconductor substrateof FIG. 1, taken along line 1-1 of FIG. 1, illustrating an exemplarymethod for forming a FinFET device;

FIG. 7 is a perspective view of the FinFET device formed in accordancewith the method shown in FIGS. 2-6; and

FIG. 8 is a cross-sectional side view of another exemplary embodiment ofa FinFET device.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the fin field-effect transistor (FinFET) devicesand methods of forming the FinFET devices as contemplated herein.Furthermore, there is no intention to be bound by any theory presentedin the preceding background or the following detailed description.

Embodiments of the present disclosure are generally directed to FinFETdevices and methods for forming the same. For the sake of brevity,conventional techniques related to FinFET device fabrication may not bedescribed in detail herein. Moreover, the various tasks and processsteps described herein may be incorporated into a more comprehensiveprocedure or process having additional steps or functionality notdescribed in detail herein. In particular, various steps in themanufacture of semiconductor-based transistors are well-known and so, inthe interest of brevity, many conventional steps will only be mentionedbriefly herein or will be omitted entirely without providing thewell-known process details.

Fin field-effect transistor (FinFET) devices and methods of forming theFinFET devices that avoid merger between epitaxially-grown sourceregions and drain regions of adjacent fins are provided herein. Inparticular, merger between an epitaxially-grown source region on one finand an epitaxially-grown source region on an immediately adjacent fin isavoided, and merger between an epitaxially-grown drain region on one finand an epitaxially-grown drain region on an immediately adjacent fin isalso avoided. Merger between the epitaxially-grown source regions anddrain regions of adjacent fins often occurs due to the manner in whichepitaxial growth of the source regions and drain region propagates, withgrowth occurring both vertically and laterally. The merger between theepitaxially-grown source regions and drain regions of adjacent fins isavoided by providing epitaxially-grown source regions and drain regionshaving an asymmetric profile along a lateral direction perpendicular toa length of the fins. By “asymmetric profile”, it is meant that theepitaxially-grown source regions and drain regions laterally protrudefrom the fin further on a first side of the fin than on a second side ofthe fin that is opposite to the first side. The asymmetric profile ofthe epitaxially-grown source regions and drain regions effectivelyincreases a distance between epitaxially-grown source regions and drainregions on adjacent fins while also maximizing available surface area ofthe epitaxially-grown source regions and drain regions for formation ofsilicide, even as line width technology continues to scale down.

Referring to FIG. 1, in accordance with an exemplary embodiment of amethod for forming a FinFET device, a semiconductor substrate 10 isprovided that has a plurality of fins 12 formed therein or thereon, withthe fins 12 disposed in parallel relationship. Although only two fins 12are shown, it is to be appreciated that the semiconductor substrate 10may include numerous additional fins 12 in accordance with conventionalFinFET technology. Without intending to be limiting, the fins 12 mayhave a width on the nanometer scale, such as from about 5 to about 20nm, although the FinFET devices and methods described herein are notlimited to any particular dimensional constraints. As used herein, theterm “semiconductor substrate” will be used to encompass semiconductormaterials that are conventionally used in the semiconductor industry.“Semiconductor materials” include monocrystalline silicon materials,such as relatively pure or lightly impurity-doped monocrystallinesilicon materials typically used in the semiconductor industry, as wellas polycrystalline silicon materials, and silicon admixed with otherelements such as germanium, carbon, and the like. In addition,“semiconductor material” encompasses other materials such as relativelypure and impurity-doped germanium, gallium arsenide, zinc oxide, glass,and the like. In the embodiment shown in FIG. 1, the semiconductorsubstrate 10 is a bulk silicon wafer with the fins 12 are formed in thebulk silicon wafer. However, it is to be appreciated that in otherembodiments and although not shown in the Figures, the semiconductorsubstrate 10 may include a silicon-containing material that is disposedon an insulating material, commonly known as a silicon-on-insulator(SOI) structure that, in turn, may be supported by a support substrate.

For illustrative purposes, only a portion 14 of the semiconductorsubstrate 10 is shown in FIG. 1. In embodiments, the fins 12 are dopedwith a dopant chosen from P-type dopants or N-type dopants in accordancewith conventional well formation. For example, in an embodiment, theportion 14 of the semiconductor substrate 10 and the fins 12 are dopedwith a P-type dopant such as, but not limited to, boron, aluminum,gallium, indium, BF₂, and combinations thereof in anticipation offorming an N-type metal oxide semiconductor (NMOS) FinFET. However, itis to be appreciated that, although not shown, other portions of thesemiconductor substrate 10 may be doped with an N-type dopant such as,but not limited to, phosphorus, arsenic, antimony, and combinationsthereof in anticipation of forming a P-type metal oxide semiconductor(PMOS) FinFET. In this regard, the methods described herein are suitablefor forming either NMOS FinFETs or PMOS FinFETs, depending upon theparticular materials that are employed for forming features of therespective FinFETs. If the FinFET device being fabricated is acomplimentary MOS integrated circuit (CMOS IC), there will be at leastone portion of the semiconductor substrate 10 and fins 12 that is dopedwith N-type dopant and at least one portion of the semiconductorsubstrate 10 and fins 12 doped with P-type dopant. The portions of thesemiconductor substrate 10 can be doped, for example, by ionimplantation prior to or after forming the fins 12 in or on thesemiconductor substrate 10, with the fins 12 including the dopant.Multiple ion implantation steps may be used to achieve a desired dopantconcentration and profile.

As shown in FIG. 1, a gate electrode structure 20 is disposed over thefins 12. For example, in an embodiment, a first insulator layer 16overlies the semiconductor substrate 10 and has a thickness that is lessthan a height of the fins 12 such that the fins 12 extend through andprotrude beyond the first insulator layer 16 to provide exposed finportions 18. As referred to herein, the terms “overlie” or “overlies”are used to encompass both “over” and “on”, with features that “overlie”other features being disposed over the other features or directly uponthe other features. The first insulator layer 16 is not particularlylimited and may include an oxide such as, for example, silicon dioxide.The gate electrode structure 20 overlies the fins 12 and, morespecifically, overlies the exposed fin portions 18. The gate electrodestructure 20 is electrically insulated from the fins 12 by a gateinsulating layer 22. In embodiments and as shown in FIG. 1, the gateelectrode structure 20 wraps around the exposed fin portions 18, onthree sides thereof, in accordance with conventional FinFET technology.The gate electrode structure 20 may be formed over the fins 12 throughconventional techniques, such as gate-first or gate-last,polysilicon/SiON or Hi-K/metal-gate techniques. For example, inembodiments, the gate electrode structure 20 is a dummy gate structureand formation of the FinFET device includes eventually replacing thedummy gate structure after formation of epitaxially-grown source regionsand drain regions, as set forth in further detail below. In anembodiment and as shown in FIG. 1, a nitride cap 24 may be disposedoverlying the gate electrode structure 20 to facilitate formation of thegate electrode structure 20 and to provide protection to the gateelectrode structure 20 during formation of the FinFET device. Thenitride cap 24 may be formed from any nitride such as, for example,silicon nitride.

FIGS. 2-6 illustrate the portion 14 of the semiconductor substrate 10 ofFIG. 1 in cross-section taken along line 1-1 for purposes ofillustrating an exemplary method of forming the FinFET device. Inaccordance with an exemplary embodiment and referring to FIGS. 2 and 3,a first intermediate sidewall spacer 26 is formed adjacent to a firstside 28 of the fins 12 and over the first insulator layer 16 and asecond intermediate sidewall spacer 30 is also formed adjacent to asecond side 32 of the fins 12 and over the first insulator layer 16. Asalluded to above, the FinFET devices may include both N-type FinFETs andP-type FinFETs. The first intermediate sidewall spacer 26 and the secondintermediate sidewall spacer 30 may be formed during formation ofconventional gate spacers (not shown) for the N-type FinFETs and P-typeFinFETs, and intermediate sidewall spacers may be formed at differentstages and locations within the FinFET devices during formation of theFinFET devices.

In embodiments and referring to FIG. 2, a hardmask layer 34 is formed byblanket depositing hardmask material over the fins 12 and the firstinsulator layer 16 as well as over the gate electrode structure (notshown in FIG. 2). Suitable hardmask materials for the hardmask layer 34include materials that have a different etch rate as compared to thefins 12 and the first insulator layer 16. For example, in embodiments,the hardmask layer 34 includes a silicon-containing dielectric materialchosen from silicon nitride, silicon oxide, silicon carbide, siliconoxycarbonitride, silicon carboxynitride, and the like. Additionally, itis to be appreciated that stacked layers formed from the aforementionedmaterials may be deposited to form the hardmask layer 34.

In embodiments, the hardmask layer 34 is patterned to form theintermediate sidewall spacers 26, 30 (as shown in FIG. 3) duringpatterning of gate spacers for P-type FinFETs or during patterning ofgate spacers for P-type FinFETs to form the intermediate sidewallspacers 26, 30. Unlike patterning of the gate spacers (not shown), whichare formed on the fins 12 and along sidewalls of the gate electrodestructure, the first intermediate sidewall spacer 26 and the secondintermediate sidewall spacer 30 as described herein are formed adjacentto the first side 28 of the fins 12 and the second side 32 of the fins12, respectively, and directly over the first insulator layer 16. Asreferred to herein, the first intermediate sidewall spacer 26 and thesecond intermediate sidewall spacer 30 are formed during the same stagefrom the same hardmask layer 34. The first intermediate sidewall spacer26 and the second intermediate sidewall spacer 30 may be concurrentlyformed with the gate spacers by appropriately masking the hardmask layer34 and anisotropically etching the hardmask layer 34 to form theintermediate sidewall spacers 26, 30 at the same time as formation ofthe gate spacers. For example, reactive ion etching (RIE) may beemployed using sulfur fluoride (SF₆) to anisotropically etch thehardmask layer 34 that includes the silicon nitride. As another example,a wet etch may be employed using a dilute solution of hydrofluoric acid(DHF) to anisotropically etch the hardmask layer 34 that includes thesilicon oxide, and the DHF may include a buffer such as ammoniumfluoride. Other conventional anisotropic etching techniques may beemployed beyond those described above and based upon the particularmaterial of the hardmask layer 34.

In embodiments, etching of the hardmask layer 34 to form theintermediate sidewall spacers 26, 30 may proceed until exposed portionsof the hardmask layer 34 are substantially removed from horizontalsurfaces, thereby exposing a top surface of the fins 12 and horizontalsurfaces of the first insulator layer 16 and resulting in the firstintermediate sidewall spacer 26 and the second intermediate sidewallspacer 30 as shown in FIG. 3.

Referring to FIGS. 3 and 4, the second intermediate sidewall spacer 30is asymmetrically etched as compared to the first intermediate sidewallspacer 26 to produce a first sidewall spacer 36 and optionally a secondsidewall spacer 38 adjacent to a source region 39 and a drain region inthe fins 12. Because FIGS. 3 and 4 are cross-sectional views, only thesource region 39 is shown, although it is to be appreciated that thefirst sidewall spacer 36 and the second sidewall spacer 38 are situatedadjacent the drain region in a similar configuration to that shown forthe source region 39 in FIGS. 3 and 4. As referred to herein,“asymmetrically etching” the second intermediate sidewall spacer 30 ascompared to the first intermediate sidewall spacer 26 encompasses anytechnique whereby the second intermediate sidewall spacer 30 is etchedat a faster rate as compared to the first intermediate sidewall spacer26, and further encompasses any technique whereby the secondintermediate sidewall spacer 30 is selectively removed while leaving thefirst intermediate sidewall spacer 26 in place to form the firstsidewall spacer 36. In embodiments and as shown in FIG. 4, the secondsidewall spacer 38 remains after asymmetric etching, although it is tobe appreciated that in other embodiments and as described in furtherdetail below, the second sidewall spacer is completely removed and isabsent after asymmetric etching with only the first sidewall spacer 36remaining.

In embodiments, the second intermediate sidewall spacer 30 isasymmetrically etched as compared to the first intermediate sidewallspacer 26 by implanting ions 42, 44 that have an impact on etchsensitivity into the first intermediate sidewall spacer 26 and/or thesecond intermediate sidewall spacer 30. In particular, ions may beimplanted that either increase or decrease sensitivity of theintermediate sidewall spacers 26, 30 to particular etchants, and theions may be implanted in a tilted direction to expose one of the firstintermediate sidewall spacer 26 or the second intermediate sidewallspacer 30 to more of the particular ion. In an embodiment, the secondintermediate sidewall spacer 30 is implanted with a higher content of afirst etch-impacting ion 42 as compared to the content of the firstetch-impacting ion 42 implanted into the first intermediate sidewallspacer 26, with the first etch-impacting ion 42 increasing an etch rateof intermediate sidewall spacers 26, 30 in the first sidewall etchant.Implanting the second intermediate sidewall spacer 30 with the highercontent of the first etch-impacting ion 42 may be accomplished byimplanting the first etch-impacting ion 42 in a tilted direction 37,relative to a vertical axis through the fin 12 and substrate 10, withimplantation directed more toward the second intermediate sidewallspacer 30 than the first intermediate sidewall spacer 26 and with thefirst intermediate sidewall spacer 26 at least partially shielded fromion implantation by the fins 12. Thus, etching of the secondintermediate sidewall spacer 30 will occur at a faster rate in theparticular first sidewall etchant as compared to an etch rate of thefirst intermediate sidewall spacer 26 due to implantation in the tilteddirection with the second intermediate sidewall spacer 30 receiving ahigher amount of the first etch-impacting ion 42 than the firstintermediate sidewall spacer 26. It is to be appreciated that topportions of the first intermediate sidewall spacer 26 may have greaterexposure to the tilted implantation of the first etch-impacting ion 42and, thus, may etch at a faster rate than lower portions of the firstintermediate sidewall spacer 26. However, on the whole, the firstintermediate sidewall spacer 26 will have a lower content of the firstetch-impacting ion 42 than the second intermediate sidewall spacer 30,thus resulting in different etch impact on the respective intermediatesidewall spacers 26, 30.

Depending upon the type of material used for the hardmask layer 34, thefollowing first etch-impacting ions 42 may be implanted to increasesensitivity of the hardmask layer 34 to particular first sidewalletchants: nitrogen (N₂), fluorine, or oxygen (O₂). Specific examples ofcombinations of materials for the hardmask layer 34 and firstetch-impacting ions 42 that increase sensitivity of the hardmask layer34 to particular etchants are as follows: for silicon nitride, N₂ may beemployed as the first etch-impacting ion 42; for silicon oxide, O₂ maybe employed as the first etch-impacting ion 42.

In another embodiment, the second intermediate sidewall spacer 30 isasymmetrically etched as compared to the first intermediate sidewallspacer 26 by asymmetrically implanting the first intermediate sidewallspacer 26 with a higher content of a second etch-impacting ion 44 ascompared to the content of the second etch-impacting ion 44 implantedinto the second intermediate sidewall spacer 30, with the secondetch-impacting ion 44 decreasing an etch rate of intermediate sidewallspacers 26, 30 in the first sidewall etchant. As with the techniquesdescribed above for implanting the second intermediate sidewall spacer30 with the higher content of the first etch-impacting ion 42, the firstintermediate sidewall spacer 26 may be implanted with the higher contentof the second etch-impacting ion 44 by implanting the secondetch-impacting ion 44 in a tilted direction with implantation directedmore toward the first intermediate sidewall spacer 26 than the secondintermediate sidewall spacer 30 and with the second intermediatesidewall spacer 30 at least partially shielded from ion implantation bythe fins 12. Thus, etching of the first intermediate sidewall spacer 26will occur at a slower rate in the particular first sidewall etchant ascompared to an etch rate of the second intermediate sidewall spacer 30due to implantation in the tilted direction with the first intermediatesidewall spacer 26 receiving a higher amount of the secondetch-impacting ion 44 than the second intermediate sidewall spacer 30.It is to be appreciated that top portions of the second intermediatesidewall spacer 30 may have greater exposure to the tilted implantationof the second etch-impacting ion 44 and, thus, may etch at a slower ratethan lower portions of the second intermediate sidewall spacer 30.However, on the whole, the second intermediate sidewall spacer 30 willhave a lower content of the second etch-impacting ion 44 than the firstintermediate sidewall spacer 26, thus resulting in different etch impacton the respective intermediate sidewall spacers 26, 30.

Depending upon the type of material used for the hardmask layer 34, thefollowing second etch-impacting ions 44 may be implanted to decreasesensitivity of the hardmask layer 34 to particular first sidewalletchants: hydrogen, carbon, or nitrogen (N₂). Specific examples ofcombinations of materials for the hardmask layer 34 and secondetch-impacting ions 44 that decrease sensitivity of the hardmask layer34 to particular etchants are as follows: for silicon nitride, hydrogenmay be employed as the first etch-impacting ion 42; for silicon oxide,N₂ may be employed as the first etch-impacting ion 42.

In embodiments, a combination of different types of ions may beimplanted into the respective first intermediate sidewall spacer 26 andthe second intermediate sidewall spacer 30 to both increase the etchrate of the second intermediate sidewall spacer 30 in the first sidewalletchant and decrease the etch rate of the first intermediate sidewallspacer 26 in the first sidewall etchant. For example, as shown in FIG.3, the first etch-impacting ion 42 may be implanted in a tilteddirection with implantation directed more toward the second intermediatesidewall spacer 30 than the first intermediate sidewall spacer 26, andthe second etch-impacting ion 44 may be implanted in another tilteddirection with implantation directed more toward the first intermediatesidewall spacer 26 than the second intermediate sidewall spacer 30.

Following ion implantation and referring to FIG. 4, the intermediatesidewall spacers 26, 30 are again etched using the same or differentetching techniques as described above for etching the hardmask layer 34to form the intermediate sidewall spacers 26, 30. The chosen etchtechnique for etching the intermediate sidewall spacers 26, 30 isdependent upon the particular etch-impacting ions 42, 44 that areemployed so as to asymmetrically etch the second intermediate sidewallspacer 30 as compared to the first intermediate sidewall spacer 26,thereby producing at least the first sidewall spacer 36 and optionallythe second sidewall spacer 38 that, when present, has a smaller profilethan the first sidewall spacer 36.

Referring to FIGS. 5 and 6, following formation of the first sidewallspacer 36 and, optionally, the second sidewall spacer 38,epitaxially-grown source regions 50 and drain regions (not shown) areformed. In embodiments and although not shown, halo and/or extensionregions for the source regions and drain regions may first be formedthrough conventional ion implantation techniques using appropriate ionsfor the particular type of transistors (i.e., P-type or N-type) that areto be formed. After forming the halo and/or extension regions, portionsof the fins 12 that are adjacent to the gate electrode structure areetched with a fin etchant to form trenches 48 in anticipation of formingepitaxially-grown source regions 50 and drain regions in the trenches48. A middle of the trenches 48 may be etched deeper than edges of thetrenches 48, resulting in the profile of the trenches 48 shown in FIG.5, which is a typical profile resulting from anisotropic etching.Appropriate fin etchants may be chosen based upon the composition of thefins 12 and the composition of the sidewall spacers 36, 38. For example,in an embodiment, a reactive ion etch with hydrofluoric acid may beemployed to selectively etch silicon in the fins 12 over sidewallspacers 36, 38 that include silicon nitride. In embodiments, theparticular etchant used may also be selective to the material of thefirst insulator layer 16, resulting in recessing of the first insulatorlayer 16 as shown in FIG. 5. However, selectivity of the fin etchant tothe material of the first insulator layer 16 is not required, and finetchants may alternatively be chosen that exhibit insubstantial etchingof the material in the first insulator layer 16.

In embodiments and referring to FIGS. 6 and 7, semiconductor material isepitaxially grown in the trenches 48 to form epitaxially-grown sourceregions 50 and epitaxially-grown drain regions 51. Epitaxial growthgenerally propagates both vertically and laterally from crystallinesemiconductor material of the semiconductor substrate 10 that is exposedin the trenches 48. The first insulator layer 16 masks the portions ofthe semiconductor substrate 10 outside of the trenches 48, and thesidewall spacers 36, 38 restrict lateral epitaxial growth of thesemiconductor material. Epitaxial growth of the semiconductor materialmay persist beyond filling of the trenches 48 to provide sufficientsurface area for later silicide formation on surfaces of theepitaxially-grown source regions 50 and drain regions 51. Due to thedynamics of epitaxial grown, the epitaxially-grown source regions 50 anddrain regions 51 are further disposed overlying a top of the firstsidewall spacer 36 and a top of the second sidewall spacer 38 whenpresent. However, due to the smaller profile of the second sidewallspacer 38 as compared to the first sidewall spacer 36, lateral epitaxialgrowth on the side of the first sidewall spacer 36 is restricted ascompared to lateral epitaxial growth on the side of the second sidewallspacer 38, thus resulting in an asymmetric profile of theepitaxially-grown along a lateral direction 52 perpendicular to a lengthof the fins 12. In particular, the epitaxially-grown source regions 50and drain regions 51 protrude less on the first side 28 of the fins 12(indicated by distance 54) than on the second side 32 of the fins 12(indicated by distance 56) along the lateral direction 52 that isperpendicular to the length of the fins 12. The asymmetric profile ofthe epitaxially-grown source regions 50 and drain regions 51 enables theepitaxially-grown source regions 50 and drain regions 51 from adjacentfin field-effect transistors on adjacent fins 12 to be isolated fromdirect physical contact by effectively lengthening a distance 58 betweenthe epitaxially-grown source regions 50 and drain regions 51 of theadjacent fin field-effect transistors, as compared to distances betweenepitaxially-grown source regions and drain regions that are formed witha symmetric profile, while maximizing available surface area of theepitaxially-grown source regions 50 and drain regions 51 for formationof silicide.

FIG. 7 illustrates an exemplary FinFET device 60 including the gateelectrode structure 20, fins 12, and epitaxially-grown source regions 50and drain regions 51. In embodiments, the gate electrode structure 20 isa dummy gate electrode structure, which may be replaced with areplacement gate structure after epitaxially growing the semiconductormaterial in the trenches 48 to form the epitaxially-grown source regions50 and drain regions 51. In other embodiments, a gate-first approach isemployed with the original gate electrode structure 20 remaining inplace after epitaxially growing the semiconductor material in thetrenches 48 to form the epitaxially-grown source regions 50 and drainregions 51. After optional replacement of the gate electrode structure20, although not shown silicide may be formed on surfaces of theepitaxially-grown source regions 50 and drain regions 51 throughconventional techniques, followed by back-end-of-line (BEOL) fabricationtechniques to connect transistors in the resulting FinFET device 60. Theresulting FinFET device 60 has a single fin transistor configuration dueto the electrical isolation of the epitaxially-grown source regions 50and drain regions 51 on adjacent fins 12. The single fin transistorconfiguration may include the gate electrode structure 20 that extendsacross multiple fins 12.

As alluded to above, in embodiments, the second sidewall spacer isoptional and may be completely removed. In particular, duringasymmetrically etching of the second intermediate sidewall spacer ascompared to the first intermediate sidewall spacer, the secondintermediate sidewall spacer may be removed such that the secondsidewall spacer is absent after asymmetric etching. Referring to FIG. 8,the resulting FinFET device 160 is free from a second sidewall spacerdisposed adjacent to the second side 32 of the fins 12. Morespecifically, no spacers are disposed adjacent to the second side 32 ofthe fins 12. In this embodiment, the epitaxially-grown source regions150 and drains regions are disposed overlying the first sidewall spacer36 on the first side 28 of the fins 12 and are further disposed directlyon the first insulator layer 16 adjacent to the second side 32 of thefins 12.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration in anyway. Rather, the foregoing detailed description will provide thoseskilled in the art with a convenient road map for implementing anexemplary embodiment. It being understood that various changes may bemade in the function and arrangement of elements described in anexemplary embodiment without departing from the scope as set forth inthe appended claims.

What is claimed is:
 1. A fin field-effect transistor device comprising:a semiconductor substrate having a plurality of fins disposed inparallel relationship; a first insulator layer overlying thesemiconductor substrate, with the fins extending through and protrudingbeyond the first insulator layer to provide exposed fin portions; a gateelectrode structure overlying the exposed fin portions and electricallyinsulated from the fins by a gate insulating layer; and a first sidewallspacer is disposed adjacent to a first side of the fins and directlyover the first insulator layer; and epitaxially-grown source regions anddrain regions disposed adjacent to the gate electrode structure; whereinthe epitaxially-grown source regions and drain regions have anasymmetric profile along a lateral direction perpendicular to a lengthof the fins, wherein portions of the epitaxially-grown source regionsand drain regions are further disposed overlying a top of the firstsidewall spacer and wherein epitaxially-grown source regions and drainregions from adjacent fin field-effect transistors on adjacent fins areisolated from direct physical contact.
 2. The fin field-effecttransistor device of claim 1, wherein the epitaxially-grown sourceregions and drain regions protrude less on a first side of the fins thanon a second side of the fins along the lateral direction perpendicularto the length of the fins.
 3. The fin field-effect transistor device ofclaim 2, free from a second sidewall spacer disposed adjacent to thesecond side of the fins.
 4. The fin field-effect transistor device ofclaim 3, wherein the epitaxially-grown source regions and drain regionsare further disposed overlying the first sidewall spacer on the firstside of the fins and directly on the first insulator layer adjacent tothe second side of the fins.
 5. The fin field-effect transistor deviceof claim 1, wherein a second sidewall spacer is disposed adjacent to asecond side of the fins and over the first insulator layer, and whereinthe second sidewall spacer is smaller than the first sidewall spacer. 6.The fin field-effect transistor device of claim 5, wherein portions ofthe epitaxially-grown source regions and drain regions are furtherdisposed overlying a top of the second sidewall spacer.
 7. The finfield-effect transistor device of claim 1, wherein a second sidewallspacer is disposed adjacent to the second side of the fins and over thefirst insulator layer, wherein the second sidewall spacer is smallerthan the first sidewall spacer, and wherein the epitaxially-grown sourceregions and drain regions protrude less on the first side of the finsthan on a second side of the fins along the lateral directionperpendicular to the length of the fins.
 8. The fin field-effecttransistor device of claim 1, wherein the fins are recessed at locationsof the epitaxially-grown source regions and drain regions and whereinthe epitaxially-grown source regions and drain regions are grown onlyfrom the recessed portions of the fins.
 9. The fin field-effecttransistor device of claim 1, wherein the fin field-effect transistordevice has a single fin transistor configuration.
 10. The finfield-effect transistor device of claim 1, wherein the device is freefrom a second sidewall spacer disposed adjacent to a second side of thefins, and wherein the epitaxially-grown source regions and drain regionsprotrude less on the first side of the fins than on a second side of thefins along the lateral direction perpendicular to the length of thefins.